From The Collaborative International Dictionary of English v.0.48 :
Gunwale \Gun"wale\, n. [Gun + wale. So named because the upper guns were pointed from it.] (Naut.) The upper edge of a vessel's or boat's side; the uppermost wale of a ship (not including the bulwarks); or that piece of timber which reaches on either side from the quarter-deck to the forecastle, being the uppermost bend, which finishes the upper works of the hull. [Written also gunnel.] [1913 Webster]From WordNet (r) 3.0 (2006) :
gunwale n 1: wale at the top of the side of boat; topmost planking of a wooden vessel [syn: gunwale, gunnel, gun rest]